This invention relates to a multi-piece solid golf ball having a solid core and a cover of at least two layers.
Golf balls are generally classified into two types: the thread-wound type comprising a core having thread rubber wound around a spherical center and a cover of balata enclosing the core, and the solid type comprising a spherical rubbery elastic core and a resin cover enclosing the core. The latter is superior in flight performance when hit. The majority of golfers are in favor of solid type balls.
However, the solid golf balls have drawbacks including a hard feel when hit and less spin susceptibility when hit with a short iron. Several attempts have been made to remedy such drawbacks, for example, by reducing the hardness of the core to allow more deformation upon hitting, or inversely, by setting the hardness of the cover relatively low. It has also been attempted to enclose the core with a cover of two inner and outer resin layers, one of which is set to a lower hardness than the other (e.g., the inner layer is set to a lower hardness than the outer layer and vice versa).
In the recent years, these devices have brought fruitful results. In particular, the softened feel on hitting and spin enhancement of the dual cover structure are remarkable. However, these devices have a propensity that the flight distance which is of most interest to golfers declines with such improvements. In the current status, the advantages of the solid structure are more or less offset.
An object of the invention is to provide a multi-piece solid golf ball which is easy to control due to high-spin receptivity as in a prior art structure, when hit with a short iron, and which travels a long distance due to restricted spin when hit with a small loft angle club like a driver.
Regarding a multi-piece solid golf ball comprising a rubbery elastic core and a cover enclosing the core and consisting of a plurality of resinous layers, the present inventor has found that the ball is improved in spin performance when among the plurality of cover layers, an outer layer disposed outermost has a thickness of less than 1 mm and a Shore D hardness of 50 to 65 and an inner layer other than the outermost layer has a thickness of 0.5 to 2.0 mm and a Shore D hardness of 40 to 55. That is, due to the synergistic cooperation of the cover inner and outer layers which are optimized relative to the elastic core, the ball has improved spin performance ensuring an increase of flight distance upon driver shots and ease of control upon approach shots. Both an increase of flight distance and an improvement in ball control are accomplished.
The invention provides a multi-piece solid golf ball comprising a rubbery elastic core and a cover enclosing the core and consisting of a plurality of resinous layers, wherein among the plurality of cover layers, an outer layer disposed outermost has a thickness of less than 1 mm and a Shore D hardness of 50 to 65 and an inner layer has a thickness of 0.5 to 2.0 mm and a Shore D hardness of 40 to 55. It is noted that the inner layer represents all cover layers disposed inside the outermost layer if the cover consists of more than two layers, as will be described later.
In a preferred embodiment, the outer layer has a higher hardness than the inner layer and/or the outer layer has a smaller thickness than the inner layer. In another preferred embodiment, the outer layer is formed primarily of an ionomer resin having a melt flow rate of at least 3.0 dg/min at a temperature of 190xc2x0 C., and the inner layer is formed primarily of a highly neutralized ionomer resin. Also preferably, the elastic core undergoes a deflection of 3.0 to 4.5 mm under an applied load of 980.7 N (100 kgf).